Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

875
FXUS63 KLOT 051751
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1151 AM CST Thu Feb 5 2026

.KEY MESSAGES...

- A clipper system will move through the region today and bring
  chances (30 to 50%) for snow showers.

- Pockets of freezing mist and drizzle may develop after
  midnight tonight. In addition, relatively moist air moving
  over the cold ground may cause condensation and subsequent
  freezing on roadways. Confidence in either scenario is low
  (<25% chance for both).

- Another clipper system will move through the region centered
  on daybreak tomorrow with a threat for a wintry mix. Locally
  hazardous travel may result.

- A sharp cold front will race through the region Friday
  evening. Snow showers, including squall-like behavior, may
  accompany the front.

- A period of nuisance lake effect snow will occur in
  northwestern Indiana Friday night through Saturday.

- A pattern shift will occur next week toward warmer, and
  potentially wetter, conditions.

&&

.DISCUSSION...
Issued at 315 AM CST Thu Feb 5 2026

There are a lot of subtleties to the forecast through the next
48 hours, so apologies for the length of the AFD.

Early morning GOES-19 water vapor imagery depicts an upper-
level shortwave diving southward from southwestern Ontario
toward western lake Superior and northeastern Minnesota.
Ensemble model guidance remains in agreement that the shortwave
will track generally just east of the Mississippi River today,
reaching northern Illinois and northwestern Indiana by mid-
morning. While the past few cycles of most model guidance has
trended toward dry low-level air eroding all precipitation by
the time the system reaches our area, the ECMWF has remained
steadfast that showery activity tied to a plume of steep mid-
level lapse rates in the core of the vorticity maxima will
survive and sweep across our area. Accordingly, will cautiously
advertise scattered showers in our forecast for much of the
area, generally in a 2 to 4 hour window from late morning to
early afternoon. Precipitation type should favor snow with the
clipper, though would not be surprised to see a few reports of
sleet due to the convective processes involved. While
temperatures will still be below freezing as the showery
activity races overhead, generally limited precipitation amounts
(<0.05" liquid equivalent) should mitigate impacts on roadways
where the precipitation does reach the ground. When also
considering temperatures will rise toward freezing in most
locations by early afternoon, the clipper today does not have
the hallmarks of being too big of an issue.

Behind the wave this evening, low-level stratus may attempt to
redevelop/lower in cloud base as low-level warm air advection
gradually increases in advance of a secondary clipper system
diving into the Great Lakes. While forecast soundings depict
generally shallow depths to the stratus layer (around 2000ft
deep), am growing increasingly concerned that pockets of
freezing mist or drizzle may emerge by midnight, especially if
cloud bases are able to lower below 1000 ft. The HRRR/RAP appear
most aggressive in showing such a scenario, actually depicting
a gradual decline in surface visibilities overnight, though
never to values below 6SM.

Making matters more complicated is the threat for the ground,
including parking lots and ground-based roadways, to "sweat"
tonight. According to the University of Illinois WARM network,
current 2-inch soil temperatures across the area are generally
in the upper 20s. The frost depth at our office remains 13
inches. As surface dew points climb into the upper 20s tonight,
the cold ground may start to condensate (much like a car
windows will fog up when driving through cold/dry conditions).
And, with temperatures remaining below freezing tonight, any
ground sweat may be prone to freezing. Confidence in this
process occurring is naturally pretty darn low especially since
dew points may warm to, but not well above, ground/soil
temperatures. Nevertheless, this sneaky phenomena has caught us
off guard in past winter seasons.

The aforementioned second clipper will race across the area
centered on daybreak tomorrow morning taking a similar track to
the first. Compared to 24 hours ago, am noting a modest
southwestward adjustment in the path of the system which would
place more of our area in line to see precipitation. So, will
gently increase PoPs to range from around 30% along a line from
Mendota to Paxton to 70% near the Lake Michigan shoreline.
Precipitation type with the second clipper looks problematic, as
the combination of robust low-level warm air advection to warm
the low-level temperature profile, mid-level drying to erode
cloud ice, and surface temperatures remaining below freezing, may
support snow transitioning to freezing rain. When also
considering the system will be rooted to a plume of steep mid-
level lapse rates, convective processes may lead to intermittent
sleet, as well. So, parts of the area (highest PoPs near the
Lake Michigan shoreline) may experience a true wintry mix
tomorrow morning centered on the morning commute.

Put altogether, do think the Friday morning commute could be
hazardous owing to a myriad of methods to make roads slippery,
including preceding freezing mist/drizzle, overnight "ground"
sweat, and an incoming wintry mix. If confidence in any of the
three mechanisms for slippery travel increases, could easily
envision the need for a Winter Weather Advisory across parts of
the area. Will let the day shift take another look given the
inherent low confidence. It does look like temperatures will
warm above freezing by mid morning, so any roadway icing should
melt by early afternoon.

If that`s not enough, am noting HRRR/RAP guidance depicting
quite a wind response behind the second clipper by mid Friday
morning, as rapid pressure rises (6mb/3hr, 10mb/6 hr) push into
the area. Forecast BUFKIT mixing profiles from either model
would support north to northwesterly gusts pushing 40 mph at
times, well above all other guidance that is more in line with
gusts in the 20 to 30 mph range. Have seen HRRR/RAP guidance
verify as too strong with winds 24 hours out beforehand, so hard
to say if they are onto something. Regardless, if the winds do
pan out, will have to watch for a legitimate snow squall set-up
Friday evening as a sharp cold front dives southward through the
Great Lakes. Such a threat would probably be highest near and
especially downwind of Lake Michigan into northwestern Indiana,
as building lake instability contributes to several hundred J/kg
of instability along the front and temperatures tumble below
freezing. Will introduce 20 to 30% PoPs across the Chicago
metropolitan area and across northwestern Indiana for this
potential for now, and let later shifts assess the threat
further.


Friday night onward:

Falling temperatures behind the cold front (850mb values
dropping toward -15C or so) and persistent north to
northwesterly winds will support the development of persistent
lake effect snow showers across northwestern Indiana Friday
night through early Saturday. Considering the inner upper-level
cyclonic shear axis will be well east of our area by then and a
surface high will be building into the Great Lakes, inversion
heights will struggle to climb beyond 5kft. Accordingly, the
lake effect snow looks more like a nuisance than an impact, with
perhaps a few inches of snow east of Gary by the time snow ends
Saturday afternoon. Elsewhere, Saturday will be a brief chilly
interlude with highs in the 20s. Thankfully, the arrival of the
surface high should lead to somewhat light winds.

Looking toward next week, a powerful 200kt+ jet streak
originating from the Kamchatka Peninsula of Russia will spur the
development of aggregate troughing along the Pacific Coast of
the US. As this occurs, a cut-off low pressure system will
develop along the southwestern US/northwestern Mexico border.
The net effect will be a substantial push of mid-level warm air
advection across the central United States, allowing for the
development of composite large-scale ridging through the Great
Lakes. Confidence hence remains high in a period of above
average temperatures next week.

Ensemble model guidance continues to exhibit a signal for the
development of a synoptic-scale cyclone somewhere in the central
US in the February 11-14 timeframe, though exactly how and
where will likely depend on the evolution of the leading cut-off
low pressure system and any ejecting shortwaves from the
aggregate troughing along the Pacific Coast.

Borchardt

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1151 AM CST Thu Feb 5 2026

Key messages for the 18Z TAF period:

* MVFR cigs throughout the period; intermittent VFR possible
  this afternoon

* A push of wintry precip tonight into early Friday with
  associated IFR possible. Mostly snow favored in Chicago with
  a period of sleet or freezing rain possible, mainly west of
  Chicago

* Additional snow showers possible around the lake Friday afternoon

MVFR cigs are expected to hang overhead throughout the period.
Bouts of VFR will be possible this afternoon before MVFR takes
hold again by this evening.

A system of wintry precip will move over the terminals late
tonight into Friday morning. At Chicago, mostly snow is favored,
but a period of sleet will also be possible. A period of
moderate to heavy snow will even be possible with <1SM
visibilities. Chicago sites may see a few tenths of accumulation
to near an inch on the high end by the time the snow wraps up
mid-morning. Sleet and freezing rain chances are higher out at
DPA and especially RFD. It`s possible that RFD sees no
measurable snow but a glaze of ice instead. Additionally, cigs
may drop into IFR territory during this period.

Expect NNW winds gusting to around 25 kt during the day on
Friday with continued MVFR cigs. An additional push of snow
showers is expected to develop over the lake and possibly bring
periods of MVFR snow to ORD, MDW, and GYY Friday afternoon.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 10 AM Friday to 3 AM CST Saturday
     for the IL nearshore waters.

     Gale Warning from noon Friday to midnight CST Friday night for
     the IN nearshore waters.

&&

$$

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